In a survey of the extracellular deoxyribonucleases found among members of the Enterobacteriaceae, it was recently reported (Rothberg and Swartz, J. Bacteriol. 90:294, 1965) that there was conclusive evidence that such activity existed in the genus Serratia, but, interestingly enough, not in Klebsiella or Aerobacter. The remaining member of Ewing and Edwards biochemical

Isolation rates of Haemophilus ducreyi from cases of chancroid are low. Experts recommend that isolation media be incubated at 33 to 35؇C, but the possible effect of this temperature range on the recovery of H. ducreyi has not been evaluated. We inoculated two sets of agar plates with material from genital ulcers and incubated one set at 33؇C and one at 35؇C; incubation at 33؇C identified 21% more cases than did incubation at 35؇C (109 versus 85 cases, respectively, of the 116 cases from which an isolation was made; P < 0.01).

Since washed cells of Lactobacillus leichmannii ATCC 7830 frequently showed erratic results in vitamin B 12 assays, a depletion technique was used to stabilize the inoculum. The method consisted of incubating the twice-washed cells at 37 C for 45 min in distilled water. Survival and growth studies indicated that the stabilizing procedure (i) did not affect cell numbers, (ii) was optimal for depleting possible carry-over of vitamin B 12 or other nutrilites and reserves, and (iii) brought about a phasing of the cells of the inoculum which underwent logarithmic growth immediately on inoculation. This minimal period (45 min) was the same when the cells were incubated in dextrose-water. Survival of the cells in physiological saline was greater than in distilled water, but a longer time was required for stabilizing the inoculum in saline, which precluded its use in routine work. The prepared inoculum showed an improvement over the washed inoculum in that readings between duplicate and triplicate tubes agreed closely and the standard curves were reproducible whether acidimetric or turbidimetric methods were followed. No erratic results were noted in more than 1 year of testing.

Since washed cells of Lactobacillus leichmannii ATCC 7830 frequently showed erratic results in vitamin B12 assays, a depletion technique was used to stabilize the inoculum. The method consisted of incubating the twice-washed cells at 37 C for 45 min in distilled water. Survival and growth studies indicated that the stabilizing procedure (i) did not affect cell numbers, (ii) was optimal for depleting possible carry-over of vitamin B12 or other nutrilites and reserves, and (iii) brought about a phasing of the cells of the inoculum which underwent logarithmic growth immediately on inoculation. This minimal period (45 min) was the same when the cells were incubated in dextrose-water. Survival of the cells in physiological saline was greater than in distilled water, but a longer time was required for stabilizing the inoculum in saline, which precluded its use in routine work. The prepared inoculum showed an improvement over the washed inoculum in that readings between duplicate and triplicate tubes agreed closely and the standard curves were reproducible whether acidimetric or turbidimetric methods were followed. No erratic results were noted in more than 1 year of testing.